It hasn't even been firmly determined that there *is* any blood on the shroud. Some tests appear to rule out the existence of actual blood, some (mostly by Heller and Adler) appear to indicate that there is blood -- but other researchers have had trouble reproducing Heller and Adler's tests even using the same methdologies.
PCR testing has amplified human DNA from the shroud (and the DNA seems to indicate an AB blood type), but there's no way to determine that the DNA traces were actually from any alleged blood on the shroud, since so many people have handled the shroud through the centuries that the source of the DNA could well have been anyone's fingerprints, hair, skin flakes, etc. which happen to have been on the surface of the shroud.
As with so many other studies of the shroud, the results are more muddled and much less conclusive than its proponents would like to admit.